The present invention relates to an arrangement for cooling a piston in a combustion engine by spraying cooling oil and particularly to the spray nozzle and to a method of forming the nozzle.
Arrangements for piston cooling in combustion engines are known whereby a lubricating oil flow is sprayed against the piston underside with the cooling purpose of preventing piston overheating. It is desirable to try to achieve as great a cooling oil flow as possible in order to bring about a corresponding large cooling effect at a given maximum pump output. The lubricating oil supply to the spray nozzle is normally provided by the engine""s ordinary lubricating oil pump, resulting in maximum pump output at high engine speed.
However, the nozzles hitherto used have resulted, at least at the maximum distance between the nozzle and the piston, in a considerable proportion of the cooling oil flow not entering the piston cooling ducts, thereby leading to low efficiency and relatively limited cooling effect. A large proportion of the oil has also been pumped round unnecessarily, leading to undesirable losses. One problem in this context is that a more comprehensive and intensive jet results in premature fragmentation of the jet, i.e. it deviates greatly from the desired, usually circular cylindrical, shape and assumes instead a conical and progressively spreading shape. The consequences include poorer directional accuracy and inferior effectiveness.
U.S. Pat. No. 4,408,575 describes an attempt to solve this problem by means of a main jet at a first velocity which is surrounded by a multiplicity of smaller jets at lower velocity. However, the solution presented in that document involves a complicated nozzle which is expensive to produce and install. A moderate spray effect may also be expected. The use of small holes also entails a large risk of obstruction. All this makes the nozzle unit proposed in that document both economically and technically disadvantageous.
One object of the present invention is to provide an arrangement of the kind mentioned in the introduction which eliminates the problems of the state of the art.
This object is achieved by the outlet end of the nozzle exhibiting an outlet aperture in the form, as seen in one cross-section, of a curved slit. This produces very good flow characteristics by preventing fragmentation of the jet. Instead, the whole jet stays largely concentrated for a long distance, even at high pump pressure, resulting in better cooling oil utilization in that a larger proportion of the cooling oil reaches the intended part of the piston and can exert there its cooling effect. This is particularly important in the case of engines with long piston strokes entailing long spraying distances, and at high pump outputs at which the jets delivered by nozzles according to the state of the art usually become prematurely fragmented.
The nozzle preferably consists of an integrated pipe section, which is easy to produce. A standard component may be used as the tube blank.
The outlet aperture preferably has a U-shaped or C-shaped cross-section so that the form of the aperture is xe2x80x9calmost circularxe2x80x9d, resulting not only in good anti-fragmentation characteristics but also in such a nozzle being economically advantageous and technically uncomplicated to produce.
Producing the nozzle by plastic forming about a mandrel which defines the shape of the outlet aperture and is preferred in connection with the invention enables the nozzle to be manufactured easily and economically and in a reliable manner. The invention also relates to a rational method for producing a nozzle for use in connection with the invention, whereby a tube blank is shaped plastically so that the resulting nozzle""s outlet aperture has a curved slit shape and preferably a U or C shape.
Further advantages are achieved by other aspects of the invention and are indicated below.